In some prior proton exchange membrane (PEM) fuel cell based power generator, a pneumatic valve is used to control a hydrogen generating chemical reaction that feeds hydrogen oxygen PEM fuel cells. The valve comprises a substantial portion of the power generator volume and weight, and thus reduces the energy density and specific energy of the power generator.
PEM fuel cells use a simple chemical reaction to combine hydrogen and oxygen into water, producing electric current in the process. Hydrogen may be produced by a chemical reaction between a fuel, such as lithium aluminum hydride and water vapor. At an anode, hydrogen molecules are ionized by a platinum catalyst, and give up electrons. The PEM allows protons to flow through, but not electrons. As a result, hydrogen ions flow through the PEM to a cathode, while electrons flow through an external circuit. As the electrons travel through the external circuit, they can perform useful work by powering an electrical device such as an electric motor, light bulb or electronic circuitry. At the cathode, the electrons and hydrogen ions combine with oxygen to form water. The byproducts of the reaction are water and heat.
In some power generators, water tends to accumulate at a cathode. The water can block pores, and hence the pathways for reactant species, leading to a decrease in power generation.